I have a 90 Grand Prix Turbo with a GT4RS Turbo set at 15 PSI of boost. Bored .30 over with polished heads, roller rockers, Comp Cam made for a 3.1 turbo. 29 Lb injectors, MSD, and a top gun chip. When I put it to the floor it spits and sputters. But if I lay into it slowly it runs fine at 15 LBs. Can some one help me?

Do you have a custom TopGun chip or just the regular one?  Without a custom chip, with those larger injectors its not going to know what to do with the fuel.  Also, the TopGun chip has a fuel cut at 13psi, so I'm not entirely sure how you're running 15, unless you've tricked the MAP sensor or something, or you again have a custom chip.  Has it been running like this since you did all the engine work?  Also, what are the specs for the GT4RS turbo, I've never heard of it before...

Shawn

Yes I have a top gun chip and no since I have done the motor work it ran fine with the original turbo. The turbo has also been changed over to vaccum no computer involvement so when its running 15 PSI the fuel pressure is still at 30 PSI. It only happenen when I put it to the floor.

Sorry its a Garrett GT45RS.

um where'd you get that turbo?

what rpm do you get boost at?

also you might be getting surge as thats a huge turbo.
I searched GT45 on google and a mustang forum came up and they were saying it was 20% to big for a 4.6L v8
also they are you'd on drag cars at 600+hp or big diesel trucks.

now I don't know what the rs stands for as google doesn't return any
results on it.

got any pics of the turbo or engine bay?



marcus

Let me get this straight. GT turbo@15 PSI, 29# injectors and 30# fuel pressure. :?:

Won't work. :roll:

The chips, stock or TG don't seem to care what size injectors your running. I ran 30# on both chips. There's 42# in it now which haven't been run yet just in the garage. (radiator is being re-cored) :(

Fuel pressure is way to low. I run 60#+ and as high as 70# at WOT. I would guess your detonating and would get it fixed pronto or you will have as many burned pistons as I do.

The difference between your old turbo and your new one is night and day.
You are prolly pumping twice the air and your fuel isn't keeping up. On a stock TGP intake system I doubt that you can run 15# with that turbo if its anything like the other GT turbos unles you can find some 120 octane
gas.

As far as fuel cut I don't know for sure if the TG chip even has it. I have run a FCD for so long I just left it on when I got the TG chip.

With the turbo and injectors you have that car should fly. If you can't do your own chip work You will have to boost the fuel with and aftermarket regulator. A good aftermarket fuel and boost gauge are mandatory.

The first thing I would do is find out why you only have 30# of fuel. Pump, filter, regulator. Stock is 40-47 at idle. It varies from there but it always goes up.

Get the boost down to managable levels and work your way back up adding fuel pressure and boost slowly.

I don't understand how you are controlling the wastegate with vacuum. :roll: Vacuum won't control a wastegate, pressure does.

Good luck an I hope this helps. let us know how you do.

Jud

Well, I don't know anything about that turbo, but if it is anything like the rest of the Garrett GT turbo line-up, that thing can support a LOT of power.  Look at this list:
http://www.atpturbo.com/root/turboinfo/gtlineup/gtlineup.htm
It starts off on the GT25R (240hp), and goes all the way up to the GT42RS (1000hp), but stops there.  I'm assuming the GT45RS is next, and if thats the case, it looks like it supports over 1000hp...meaning its definately WAY too big for that car.

But anyways, definately sounds like a fueling issue.  You need to get that fuel pressure a lot higher than that!

Shawn

check your TPS consistancy. Remove any MAP "tricks" or "ziners". Check for black smoke comming out the exhaust when its sputtering. Duble check your plugs, fuel press should be 40+psi at boost, check to see if your chip was calabrated for those injectors. This chip or 2bar setup will cut your fun at 14.5 psi (FF). I think I remembered thats all the ecm will tune to. Finaly remove that MSD crap and run the stock parts.

With some chip tunning..you can eleminate boost cut but you'd have to run rich a 14.5 psi to run to 15 or 17 psi safely.

First off, Welcome to the board! Second, please check the turbocharger again, I don't believe a "GT45RS" is even made, and if it was(judging by how Garrett names there GT series), you would have a turbo that belongs on a say a 1200hp+ car. :shock: I doubt a small little 3.1 could generate enough exhaust to turn one of those big turbos. :?:

Why would I want to get rid of the MSD? I have a hotter spark with the MSD box and coils. I am almost ready to junk the computer and go with Holleys comp, but thats alot of money. I will look at the turbo but I am almost positve thats what it is. If I can get it runnig properly, I'm hoping for at least 25#. It does run at 45# of fuel at idle though, sorry.

Is there another way to put more than 14.5# without junking the comp? Becaus emy gauge is reading 15#, but the turbo is not hooked up factory.

What boost gauge are you getting the reading off of?  Stock or aftermarket?  

Also, the stock coils provide plenty of spark for making the kind of power you want to make.  Aftermarket ones usually just cause problems.  These engines have the same coils as the L67's, and there are people running low 10's with no problems on the stock coils.  Just get rid of the MSD coils.

But yes, you can run more than 1 bar (~14.7psi) boost on the stock computer, you just have to program it for as much fuel as you would need for the peak boost you want for 14.7psi, because it uses the highest value for boost over 1 bar.  So if you want to run 20psi, then when the computer sees 14.7psi it is using the correct amount of fuel for 20psi.

But please, double check the turbo to see what kind it is.  I'm doubting that if it is the turbo you say it is, that it would even spool at all.  

Shawn

My bad, it's a GT28RS. And the boost I am reading is from a aftermarket Auto Gauge. The stock one is off the charts. Also should I get rid of the MSD all to gether or just the coils?

GT28RS is a big difference, that is a very good turbo for this size engine, should spool well and provide plenty of boost.  I would get rid of the MSD all together and run all stock ignition components (besides plugs and maybe wires).  

Shawn

Sell the MSD(including the MSD coils) and put all the stock stuff back on.  Like dbtk2 stated the stock ignition is very good from the factory so no purpose in upgrading a system that doesn't need it.  I would sell the MSD stuff and work on getting a custom tuned chip as as possible since you've changed a lot.  I would also not run anymore than 11-12 psi if you don't know how the engine is running via monitering/logging of some kind.  The TopGun chip actually runs less timing as you increase the boost past 11.6 psi so there's no point to running more until you tune it anyways.  Also, the stock computer is better than an Holley computer you could put on it.  A little harder to tune, but still better in my opinion.   :P

I'm guessing that you're running a manual boost controller, correct??  I know that I tried to run a manual controller once and when I would get on it from a stop it would do as you described(sputter).  Do you still have the factory boost control solenoid??  If so, maybe reinstall it and see if it runs any different.  I'm not saying the boost controller is the problem, but it 's one thing you can rule out if it not.   8)